A typical electronic device contains many components spaced closely together on a printed circuit board (PCB). In some designs, the PCB contains components sensitive to radio-frequency (RF) signals and enclosed within RF shields that protect them from RF signals. Generally, in these designs the RF shield is soldered to the PCB at an RF-shield contact pad on the PCB, thereby both securing the RF shield to the PCB and grounding it to the PCB ground.
When the RF-sensitive components must be reworked, by repairing and replacing them or by substituting new components, these RF shields are removed from the RF-shield pad. The shield pad is “dressed” to remove excess solder from it. As one example, an operator places the hot tip of a desoldering iron adjacent to the solder to melt the solder and then vacuums the melted solder from the RF-shield pad. After the components have been reworked, fresh solder paste is applied to the RF-shield pad, the RF shield is replaced at the RF-shield pad, and the entire PCB is subject to a reflow process to securely reattach the RF shield to the RF-shield pad.
There are several drawbacks to dressing RF-shield pads in this manner. The operator might not remove all or a sufficient amount of the solder, leaving residue solder on the RF-shield pad. The residue solder forms an uneven surface on the PCB, which can damage a nozzle dispensing solder paste for the reflow process. During the reflow process, the residue solder can flow and electrically couple adjacent components, shorting these components together. When the residue solder and fresh solder paste harden, the resulting seal between the RF shield and RF-shield pad might have gaps, exposing the RF-sensitive components to RF signals when the electronic device is being used. During the reflow process, the residue solder might decrease the strength or integrity of the seal. Finally, components on the PCB can be damaged if inadvertently touched by the hot tip of a soldering iron. All of these drawbacks make this method of dressing less reliable, more time-consuming, and, thus, more expensive.